Table of Contents

📖 Master Python Dictionaries with M.A.G.I.C.S.

Dictionaries (Hash Maps) are the “Heavyweight Champions” of Python data structures. They are used everywhere: from JSON APIs to databases and data science.

If a List is a bookshelf where you find books by number (Index), a Dictionary is a real dictionary where you find definitions (Values) by looking up a word (Key).

The Framework

Letter	Category	Meaning	Key Methods (.)	Key Functions ()
M	Make	Create / Copy	`.fromkeys()`, `.copy()`	`{}`, `dict()`
A	Add	Insert Items	`d[k]=v`, `.update()`	(None)
G	Get	Access / Find	`.get()`, `.keys()`	`len()`, `in`
I	Improve	Modify / Merge	`d[k]=v`, `.update()`	`
C	Clean	Delete / Remove	`.pop()`, `.clear()`	`del`
S	Special	Loop / View	`.items()`, `.values()`	`list(d)`

🟢 1. M – MAKE (Creation)

Keys must be unique and immutable (Strings, Numbers, Tuples).

Operation	Syntax	Example	Result
Manual Dict	`{k: v}`	`d = {'a': 1, 'b': 2}`	`{'a': 1, 'b': 2}`
Empty	`{}`	`d = {}`	`{}`
Constructor	`dict()`	`d = dict(name="Ali", age=20)`	`{'name':'Ali'...}` (Clean!)
From List	`dict(list)`	`d = dict([('a', 1), ('b', 2)])`	Converts tuples to dict.
Default	`.fromkeys()`	`d = dict.fromkeys(['a','b'], 0)`	`{'a': 0, 'b': 0}`
Comprehension	`{k:v for..}`	`d = {x: x*2 for x in range(3)}`	`{0:0, 1:2, 2:4}`

🔵 2. A – ADD (Growth)

Adding and Updating look exactly the same in dictionaries.

Operation	Syntax	Example	Result
Add One	`d[key] = val`	`d['Color'] = 'Red'`	Adds new key ‘Color’.
Merge	`.update(d2)`	`d.update({'Size': 'L'})`	Merges new dict into old one.
Set Default	`.setdefault()`	`d.setdefault('Color', 'Blue')`	Adds ‘Blue’ ONLY if ‘Color’ is missing.

🟡 3. G – GET (Access & Find)

The #1 Rule: Never trust that a key exists. Use .get() instead of [] to prevent crashes.

Operation	Syntax	Example	Result
Direct (Unsafe)	`d[key]`	`v = d['name']`	Returns value. Crashes if missing.
Safe Access	`.get(key)`	`v = d.get('name')`	Returns `None` if missing (Safe).
Get Default	`.get(k, def)`	`v = d.get('job', 'N/A')`	Returns ‘N/A’ if ‘job’ is missing.
Check Key	`key in d`	`'age' in d`	`True` / `False`
List Keys	`.keys()`	`k = d.keys()`	View of all keys `['a', 'b']`.
List Values	`.values()`	`v = d.values()`	View of all values `[1, 2]`.

🟠 4. I – IMPROVE (Modify)

How to update existing data.

Operation	Syntax	Example	Result
Overwrite	`d[key] = val`	`d['age'] = 21`	Changes ‘age’ from 20 to 21.
Bulk Update	`.update(d2)`	`d.update({'age': 22})`	Updates ‘age’ from another dict.
Merge (New)	`d1	d2`	`d3 = d1

🔴 5. C – CLEAN (Deletion)

Be careful: pop() works differently here than in lists.

Operation	Syntax	Example	Result
Pop Key	`.pop(key)`	`v = d.pop('age')`	Removes ‘age’ and returns value (20).
Pop Safe	`.pop(k, def)`	`d.pop('job', None)`	Returns `None` if missing (Safe).
Pop Last	`.popitem()`	`item = d.popitem()`	Removes & returns last added pair.
Delete	`del d[key]`	`del d['name']`	Deletes key ‘name’.
Clear	`.clear()`	`d.clear()`	Empties dict `{}`.

🟣 6. S – SPECIAL (Looping Views)

Instead of “Stats”, Dictionaries have “Views” (Items).

Operation	Syntax	Example	Result
Items	`.items()`	`list(d.items())`	`[('name', 'Ali'), ('age', 20)]`
Loop Keys	`for k in d:`	`for k in d: print(k)`	Loops through keys (Default).
Loop Both	`for k,v in...`	`for k,v in d.items():`	Crucial: Access Key and Value in loop.

⭐ PRO TIPS (Write Code Like an Expert)

Feature	Code Example	Why use it?
Safe Get	`d.get('key', 'N/A')`	Avoids `KeyError`. Always use this for optional data.
Loop Unpacking	`for k, v in d.items():`	The clean way to iterate. Don’t use `d[k]` inside a loop!
Sort by Key	`sorted(d)`	Returns a sorted list of keys.
Sort by Value	`sorted(d.items(), key=lambda x: x[1])`	Advanced: Sorts the dictionary by its values.
Merge Operator	`d3 = d1	d2`
Pretty Print	`json.dumps(d, indent=2)`	Prints nested dicts in a readable JSON format.

🆚 Quick Interview Comparison

Method A	Method B	Key Difference
`d['key']`	`d.get('key')`	[] crashes if key is missing. .get() returns None (Safe).
`del d['k']`	`d.pop('k')`	del just deletes. pop deletes AND gives you the value back.
`.keys()`	`list(d)`	.keys() returns a dynamic “View”. list(d) creates a static list of keys.

Master Python Dictionaries in 10 Minutes: The Ultimate M.A.G.I.C.S. Cheat Sheet

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Python Dictionary Methods, Python Dict Get, Python Dictionary Operations, Python Hash Map, Python Interview Questions